In the past, the furniture manufacturing industry has used tool cutter heads of the milling type carrying a plurality of form cutter blades specially shaped to impart a scroll-like or other intricate ornamental design to a wooden workpiece. Usually, a plurality of cutter heads are individually mounted on a machine tool arbor or spindle by expandable locking collars inserted into opposite ends of the spindle-receiving bore of each cutter head. The locking collars include a tubular portion that extends into the cutter head bore and a radial flange which is fastened to the end of the cutter head. The tubular portion of each collar cooperates with the wall forming the spindle-receiving bore to provide a chamber into which a fluid pressure medium, typically grease, is introduced under suitable pressure to expand the locking collar against the spindle and thereby lock the cutter head on the spindle.
Typically, the cutter head includes a radially extending main fluid pressure supply bore in communication at one end with the fluid pressure chamber of the locking collar and terminating at the other end in a grease fitting through which grease is introduced into the bore. Pressure on each locking collar is controlled by individual threaded set screws on opposite ends of the cutter head received in axial bores extending from each main supply bore. The set screws are simply advanced or withdrawn in their respective axial bores in the manner of a piston to adjust the locking pressure to a preselected value determined empirically to be sufficient for fixing the cutter head on the spindle but limited so as not to damage or deform the components.
A problem experienced in the past with this type of cutter head locking arrangement has been associated with gradual loss of locking pressure over time to a level which is insufficient to lock the cutter head firmly on the spindle and the lack of a means on the cutter head for indicating to a machine operator that this pressure loss has occurred. As a result, machine operators have started cutter machines with insufficient locking pressure applied on one or more cutter heads. In this situation, the affected cutter head does not rotate with the spindle and has severely galled the spindle and may even damage adjacent cutter heads, causing costly repairs and down time. What is needed is a means by which the machine operator can verify whether the locking pressure is being maintained at the preselected value from one day to the next or from one manufacturing run to the next to insure that each cutter head is properly locked to the spindle.